I also have very mixed results with Humbrol clear finish. I always used the spray cans and it seems to me that Humbrol just 're-organised' the quality-control department: I had already grown used to the fact that half of the cans don't spray at all (I have to lie the nozzles in a cleaner bath first and sometimes even that won't help), but now it turns out that the actual quality of the paint differs between cans. I experienced the orange-peel effect on a Revell-coat (on which I have always used a Humbrol clear coat without problems, and also a coat from a can with gloss paint suddenly gives a matt finish; wrong sticker I'm affraid...
I envy you Americans with your Future clear coats, because I have never seen something by that name in Europe. Any idea under what name it might be sold here?
Thanks in advance, regards, Gertjan